Hey,
I decided to give a try at AR+SDO+AI.

I set ALLOW_REINFORCEMENTS = FALSE in my Ja2_Options.INI but there are still reinforcements between sectors.
How do you disable them for good ?

Which lives in another thread.

Try TACTICAL_REINFORCEMENTS = FALSE

And read the mod docs in the docs folder, this version is very different from stock 1.13.

new options.txt

I don't have such file.

Here is the install I did :

- Official installer
- JA2_113_FullRelease_English_7435.exe
- JA2_113_UpdateForRelease7435_English_7609.exe
- Unpack 7609en+Modpack.7z in game folder
- Running ja2_7609en+AI_r1528.exe

Did I miss a step ?

You messed the install completely. There is detailed instruction how to use modpack.

1. Make a clean install of vanilla Jagged Alliance 2
2. Unpack 7609en+Modpack.7z into game folder
3. Select mod from Ja2.ini or use INI Editor to select mod and screen resolution
4. Run Ja2.exe or Ja2+AI.exe

What's wrong ?

- JA2_113_FullRelease_English_7435.exe
- JA2_113_UpdateForRelease7435_English_7609.exe

why it's so hard to just read and follow instructions?

I believe in order to disable reinforcements you have to go into the difficulty Settings xml file in the 1.13 Table Data folder and disable reinforcements under the specific difficulty you want to play

I believe allow reinforcements in the ini file only effects allied militia in cities